The preparation of amines from isocyanates dates back to the late 1800's and several methods have been exercised. For example, Hofmann, Ann. Chem. Pharm., 74:13 (1850) described the reaction of isocyanates with hydrochloric or sulphuric acid resulting in substantially quantitative yields of the amine salt and Gumpert, J. F. Prakt. Chemie, 31:121 (1885) described the hydrolysis of isocyanates to amines using an alkali hydroxide solution. Naegeli and Tyabji, Helv. Chim. Acta. 16:349 (1933) examined Gumpert's reaction and discovered that a carbamic acid salt is formed as an intermediate. Further, U.S. Pat. Nos. 4,386,218; 4,418,160; 4,501,873; 4,569,982; 4,540,720; 4,565,645; and 4,515,982, issued to Rasshofer et al., disclose the production of polyamines by the alkaline hydrolysis of compounds containing terminal isocyanate groups, including isocyanate prepolymers.
Chlorotoluenediamine has been produced from chlorotoluene diisocyanate as disclosed by U.S. Pat. No. 3,752,790, issued to McShane et al. McShane, however, first chlorinates the diisocyanate and then hydrolyzes the isocyanate groups with strong mineral acids, which are difficult to handle.
The production of N-formyl compounds from formamide and a primary or secondary alkyl or aryl amine using boric acid as a catalyst has been described in U.S. Pat. No. 3,347,916, issued to Huber. In addition, the reaction of aryl isocyanates with formic acid in the absence of a boron compound has been studied to some extent. U.S. Pat. No. 4,417,001, issued to Liessem, for example, describes the use of carbon dioxide generated from a carboxylic acid/isocyanate reaction as a polyurethane foam blowing agent. Similarly, U.S. Pat. No. 3,350,438, issued to Hennig, describes a process for the preparation of a biuret polyisocyanate by reacting organic polyisocyanate with anhydrous formic acid.
Further, U.S. Pat. No. 3,799,963, issued to Adams, describes a process for reducing the hydrolyzable chloride and acidic content of an organic isocyanate. The process comprises heating the organic isocyanate to a temperature above about 100.degree. C. but below the decomposition temperature of the organic isocyanate in the presence of formic acid or a formic acid derivative selected from the group consisting of N,N'-diformyl-toluenediamine, an adduct of toluenediisocyanate and formic acid. The toluene diisocyanate (TDI)-formic acid adduct, described in Adams' Example 6, for example, was prepared by reacting 80/20 2,4-/2,6-TDI with anhydrous formic acid in anhydrous ether. A white precipitate was filtered and washed with ether, yielding a white crystal having a melting point of 96.degree.-97.degree. C., which by elemental analysis had the empirical formula C.sub.10 H.sub.8 N.sub.2 O.sub.4 rather than the monoformamide C.sub.9 H.sub.8 N.sub.2 O.sub.2 or the diformamide, C.sub.9 H.sub.10 N.sub.2 O.sub.2. Our efforts to repeat this isolation have indicated that an adduct is not formed, but a formamide results.
U.S. Pat. No. 4,105,686, issued to Raes et al., describes the use of carboxylic acids to deactivate a toluenediisocyanate distillation residue to an inert granular solid at elevated temperatures from 120.degree. C. to about 200.degree. C. No product composition or structure is discussed.
Potts and Stalioraitis, in their U.S. Pat. No. 3,592,854, describe a process to hydrolyze amides to amines using water and caustic in large amounts of a lower aliphatic primary alcohol. U.S. Pat. No. 3,922,304, issued to Schreyer, similarly describes the conversion of formanilides to amines by hydrolysis or alcoholysis.
None of the prior art methods involve the preparation of phenyl amines from isocyanate, formic acid or water and a boron complexing agent. Moreover, the methods of the prior art require expensive and difficult to use reagents, which generally produce poor yields and high by-product formation.
In view of the serious deficiencies and inefficiencies of the prior art, it would be desirable to have a method to produce N-phenyl amines efficiently, cheaply and with little or no byproduct formation.